Connect back to SOCKS4 server

# SPDX-FileCopyrightText: 2005 Michel Arboi
# Some text descriptions might be excerpted from (a) referenced
# source(s), and are Copyright (C) by the respective right holder(s).
#
# SPDX-License-Identifier: GPL-2.0-only

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.17155");
  script_version("2025-12-17T05:46:28+0000");
  script_tag(name:"last_modification", value:"2025-12-17 05:46:28 +0000 (Wed, 17 Dec 2025)");
  script_tag(name:"creation_date", value:"2005-11-03 14:08:04 +0100 (Thu, 03 Nov 2005)");
  script_tag(name:"cvss_base", value:"5.1");
  script_tag(name:"cvss_base_vector", value:"AV:N/AC:H/Au:N/C:P/I:P/A:P");
  script_name("Connect back to SOCKS4 server");
  script_category(ACT_ATTACK);
  script_copyright("Copyright (C) 2005 Michel Arboi");
  script_family("Denial of Service");
  script_dependencies("socks.nasl");
  script_require_ports("Services/socks4", 1080);
  script_mandatory_keys("socks4/detected");

  script_tag(name:"summary", value:"It was possible to connect to the SOCKS4 server
  through itself.");

  script_tag(name:"impact", value:"This allows anybody to saturate the proxy CPU, memory or
  file descriptors.");

  script_tag(name:"solution", value:"Reconfigure your proxy so that it refuses connections to itself");

  script_tag(name:"solution_type", value:"Mitigation");
  script_tag(name:"qod_type", value:"remote_vul");

  exit(0);
}

include("misc_func.inc");
include("port_service_func.inc");

port = service_get_port(default:1080, proto:"socks4");
s = open_sock_tcp(port);
if(!s)
  exit(0);

p2 = port % 256;
p1 = port / 256;
a = split(get_host_ip(), sep: '.');

cmd = raw_string(4, 1, p1, p2, int(a[0]), int(a[1]), int(a[2]), int(a[3])) + "root" + '\0';
for (i = 3; i >= 0; i--) {
  send(socket: s, data: cmd);
  data = recv(socket: s, length: 8, min: 8);
  if (strlen(data) != 8 || ord(data[0]) != 4 || ord(data[1]) != 90) break;
}

close(s);
if(i < 0) {
  security_message(port:port);
  exit(0);
}

exit(99);